Methods and system for diagnosing fuel injectors of an engine

ABSTRACT

Various methods and systems are provided for diagnosing a condition of a fuel injector of an engine. In one example, a method for an engine includes injecting a first pulse of fuel as a first pilot injection into a first subset of cylinders of a plurality of engine cylinders, where the first pilot injection precedes a primary injection of fuel into the first subset of cylinders by a duration; correlating a first response in an engine operating parameter to the first pilot injection; and adjusting the primary injection of fuel into the first subset of cylinders based on the first response. In one example, the first pilot injection precedes the primary injection by a predefined short duration and the primary injection of fuel is adjusted within a predefined or preset upper limit and lower limit.

BACKGROUND Technical Field

Embodiments of the subject matter disclosed herein relate to an enginesystem including fuel injectors and diagnosing a condition of the fuelinjectors based on a response in an engine operating parameter(following injecting fuel with the fuel injectors).

DISCUSSION OF ART

An engine, such as a diesel engine, may include a fuel system includinga plurality of fuel injectors. In one example, one fuel injector may becoupled to each cylinder of the multi-cylinder engine. Each fuelinjector may be adapted to inject a pulse of fuel into the cylinder at adifferent time in an engine cycle, according to a cylinder firing orderof the engine. A controller of the engine may assume a uniform injectorhealth over the life of the injector and may not distinguish betweennewer and older injectors. As such, fuel injection parameters of theengine may remain the same throughout a lifetime of use of the injector.However, over time, one or more of the injectors may age or becomedegraded (e.g., faulty) which may cause the one or more injectors toinject more or less fuel than expected (or commanded). As a result,engine emissions may increase and performance of the engine maydecrease.

BRIEF DESCRIPTION

In one embodiment, a method for an engine (e.g., a method forcontrolling an engine system) comprises injecting a first pulse of fuelas a first pilot injection into a first subset of cylinders of aplurality of engine cylinders, where the first pilot injection precedesa primary injection of fuel into the first subset of cylinders by aduration; correlating a first response in an engine operating parameterto the first pilot injection; and adjusting the primary injection offuel into the first subset of cylinders based on the first response.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic diagram of a vehicle with an engine accordingto an embodiment of the disclosure.

FIG. 2 shows a schematic diagram of a cylinder of the engine of FIG. 1,according to an embodiment of the disclosure.

FIG. 3 shows a flow chart of a method for adjusting fuel injection viaone or more fuel injectors based on a response in an engine operatingparameter following a fuel injector injection event, according to anembodiment of the disclosure.

FIG. 4 shows a flow chart of a method for diagnosing a condition of afuel injector based on a response in an engine operating parameterfollowing performing a pilot injection with the fuel injector, accordingto an embodiment of the disclosure.

FIG. 5 shows a flow chart of a method for diagnosing a condition of oneor more fuel injectors based on variations in engine speed accelerationsafter injecting fuel into each cylinder, according to an embodiment ofthe disclosure.

FIG. 6 shows a graph of changes to an effective pulse width of a fuelinjector over time and a number of pilot injection events, according toan embodiment of the disclosure.

FIG. 7 shows a graph of performing pilot injections at differentcylinders during different engine cycles and adjusting subsequent fuelinjection events based on a response in an engine operating parameterdue to the pilot injections, according to an embodiment of theinvention.

DETAILED DESCRIPTION

The following description relates to embodiments of diagnosing acondition of one or more fuel injectors based on a response in an engineoperating parameter following a fuel injection event of the one or morefuel injectors. In one embodiment, a method for an engine includesinjecting a first pulse of fuel as a first pilot injection into a firstsubset of cylinders of a plurality of engine cylinders, where the firstpilot injection precedes a primary injection of fuel into the firstsubset of cylinders by a pre-set duration; correlating a first responsein an engine operating parameter to the first pilot injection; andadjusting the primary injection of fuel into the first subset ofcylinders based on the first response. In one example, the engineoperating parameter may be engine speed. In another example, the engineoperating parameter may be engine knock. In yet another example, theengine operating parameter may be engine misfire. In yet anotherexample, the engine operating parameter may be engine (individualcylinder generated) torque. A condition of a first fuel injectorinjecting the first pulse of fuel may be diagnosed based on a change inthe first response over a number of first pilot injections. In adifferent embodiment, where engine instantaneous torque can be measured,a method for an engine includes injecting fuel into each cylinder of aplurality of cylinders of the engine over a single engine cycle via aplurality of fuel injectors, where each fuel injector of the pluralityof fuel injectors is coupled to a different cylinder of the plurality ofcylinders; determining individual torque output resulting from theinjection of fuel into each cylinder; and indicating degradation of oneor more of the plurality of fuel injectors in response to a variation inthe determined individual engine (cylinder) torque output being greaterthan a threshold torque level. In yet another embodiment, a method foran engine includes injecting fuel into each cylinder of a plurality ofcylinders of the engine over a single engine cycle via a plurality offuel injectors, where each fuel injector of the plurality of fuelinjectors is coupled to a different cylinder of the plurality ofcylinders; determining individual engine speed accelerations resultingfrom the injection of fuel into each cylinder; and indicatingdegradation of one or more of the plurality of fuel injectors inresponse to a variation in the determined individual engine speedaccelerations being greater than a threshold acceleration level.

FIG. 1 shows an engine including a plurality of cylinders, each cylinderincluding a fuel injector. Each time one of the fuel injector fires(e.g., injects fuel into the cylinder which it is coupled to), a speedof the engine (e.g., engine speed) may increase. For example, a spike inengine speed from a baseline (just prior to injector firing) enginespeed may occur following an injection of fuel into an engine cylinder.The increase in engine speed may be measured via an engine speed sensor,such as the crankshaft speed sensor shown in FIG. 2. As a fuel injectorages or becomes degraded, it may inject a different fuel amount thancommanded in response to a control signal sent to the fuel injector. Bymonitoring changes in an operating parameter of the engine, such asengine speed, engine torque output, engine knock, or engine misfire, achange in performance (from a baseline or commanded value) may bedetermined, thereby enabling diagnosis of the fuel injectors. In oneexample, as shown in the method of FIG. 4, a pilot injection may bedelivered via a single fuel injector and a response in an engineoperating parameter as a result of the pilot injection may be used todiagnose the fuel injector. For example, as shown in FIG. 6, the fuelinjector may be diagnosed based on changes to an effective pulse widthof the pilot injection of the fuel injector over time, where theeffective pulse width is determined based on the response in the engineoperating parameter. Further, as shown in FIG. 7, the method shown inFIG. 4 may be repeated during different engine cycles for each fuelinjector and the corresponding cylinder which the fuel injector iscoupled to. In another example, as shown in the method of FIG. 5, aprimary injection of fuel may be delivered to each cylinder via the fuelinjectors and the individual engine speed accelerations resulting fromthe injection of fuel into each cylinder may be compared between thecylinders. The variation in engine speed acceleration between eachcylinder, the individual engine speed acceleration values, and a knownfiring order of the engine cylinders may then be used to diagnose thefuel injectors and to identify/determine which specific fuel injector orinjectors are degraded and injecting less fuel or more fuel, outside ofthe allowable tolerance. Additionally, as shown in the method of FIG. 3,fuel injection via the fuel injectors (e.g., the amount or pulse widthof fuel injected) may then be adjusted based on the diagnosis of thefuel injectors and/or the determined engine parameter responses. In thisway, a change in performance of one or more fuel injectors may bediagnosed and engine operation may be adjusted to account for the changein performance. As a result, engine emissions may be maintained at adesired level and engine performance and efficiency may be increased.

The approach described herein may be employed in a variety of enginetypes, and a variety of engine-driven systems. Some of these systems maybe stationary, while others may be on semi-mobile or mobile platforms.Semi-mobile platforms may be relocated between operational periods, suchas mounted on flatbed trailers. Mobile platforms include self-propelledvehicles. Such vehicles can include on-road transportation vehicles, aswell as mining equipment, marine vessels, rail vehicles, and otheroff-highway vehicles (OHV). For clarity of illustration, a locomotive isprovided as an example of a mobile platform supporting a systemincorporating an embodiment of the invention.

Before further discussion of the approach for diagnosing a change inperformance of fuel injectors of an engine, an example of a platform isdisclosed in which the engine may be installed in a vehicle, such as arail vehicle. FIG. 1 shows a block diagram of an embodiment of a vehiclesystem 100 (e.g., a locomotive system), herein depicted as vehicle 106.The illustrated vehicle is a rail vehicle configured to run on a rail102 via a plurality of wheels 112. As depicted, the vehicle includes anengine system with an engine 104. In one embodiment herein, the engineis a multi-fuel engine operating with diesel fuel and natural gas, butin other examples the engine may use various combinations of fuels otherthan diesel and natural gas (such as any combination of diesel,gasoline, natural gas, or other fuel blends). In yet another embodiment,the engine may be a single-fuel engine operating with only one fuel,such as diesel fuel or direct injection of gasoline (such as GDI) ordirect injection of natural gas injected (such as HPDIGAS) into theengine cylinder.

The engine receives intake air for combustion from an intake passage114. The intake passage receives ambient air from an air filter (notshown) that filters air from outside of the vehicle. Exhaust gasresulting from combustion in the engine is supplied to an exhaustpassage 116. Exhaust gas flows through the exhaust passage, and out ofan exhaust stack of the vehicle.

The engine system includes a turbocharger 120 (“TURBO”) that is arrangedbetween the intake passage and the exhaust passage. The turbochargerincreases air charge of ambient air drawn into the intake passage inorder to provide greater charge density during combustion to increasepower output and/or engine-operating efficiency. The turbocharger mayinclude a compressor (not shown in FIG. 1) which is at least partiallydriven by a turbine (not shown in FIG. 1). While in this case a singleturbocharger is shown, other systems may include multiple turbine and/orcompressor stages. In other embodiments, the engine system may benaturally aspirated receiving fresh air charge for in-cylindercombustion and not include a turbocharger.

In some embodiments, the engine system may include an exhaust gastreatment system coupled in the exhaust passage upstream or downstreamof the turbocharger. In one example embodiment having a diesel engine,the exhaust gas treatment system may include a diesel oxidation catalyst(DOC) and a diesel particulate filter (DPF). In other embodiments, theexhaust gas treatment system may additionally or alternatively includeone or more emission control devices. Such emission control devices mayinclude a selective catalytic reduction (SCR) catalyst, three-waycatalyst, NOx trap, as well as filters or other systems and devices.

A controller (e.g., electronic controller having one or more processors)148 may be employed to control various components related to the vehiclesystem. In one example, the controller includes a computer controlsystem. The controller further includes computer readable storage media(e.g., memory) including code for enabling on-board monitoring andcontrol of rail vehicle operation. The controller, while overseeingcontrol and management of the vehicle system, may receive signals from avariety of sensors 150, as further elaborated herein, to determineoperating parameters and operating conditions, and correspondinglyadjust various engine actuators 152 to control operation of the vehicle.For example, the controller may receive signals from various enginesensors including, but not limited to, engine speed, engine torqueoutput, engine load, boost pressure, exhaust pressure, ambient pressure,exhaust temperature, knock, misfire, and the like. Correspondingly, thecontroller may control aspects and operations of the vehicle system bysending commands to various components such as traction motors,alternator or generator, cylinder valves, air and/or fuel throttle, fuelinjectors, and the like.

As shown in FIG. 1, the engine includes a plurality of cylinders 108.Though FIG. 1 depicts an engine with eight cylinders, other numbers ofcylinders are possible. Each cylinder of the engine may include a knocksensor 110 and a fuel injector 111. Each fuel injector may inject fuelinto the cylinder which it is coupled to at a different time than theother fuel injectors. The order in which each fuel injector fires (e.g.,injects fuel into the corresponding cylinder) may be referred to hereinas the cylinder firing order. For a single engine cycle, each fuelinjector may fire at a different time within the cylinder firing order.For example, each fuel injector may deliver one primary injection intothe cylinder which it is coupled to in a single engine cycle. In someembodiments, as described further below, one fuel injector of onecylinder for the single engine cycle may additionally perform a pilotinjection, before its primary injection, in order to diagnose theperformance of the fuel injector (as described further below withreference to FIGS. 3-4 and 6-7).

In some embodiments, as shown in FIG. 1, the engine includes one enginecrankshaft torque output sensor 113 for the entire engine, and a torquecontribution to the crankshaft from each individual cylinder can bemeasured and determined based on torque data associated with thespecific contributing cylinder. In one example, the torque sensor may bea contact type or contactless type or slip-ring type. Each of the typesmay use strain gauge, piezo-electric, or such other technologies. Thetorque sensor may output a voltage which is then received as a voltagesignal at the controller. In one embodiment, the controller processesthe voltage signal from the torque sensor to determine a correspondingcylinder-by-cylinder torque output for the entire engine, for each fullcycle of engine operation, and subsequently adjust engine operationbased on the received data. In another example, the controller maydetermine cylinder misfire based on the output of the torque sensor, acrankshaft position output (e.g., via a crankshaft position or speedsensor, as shown in FIG. 2 and described further below), and a knowncylinder firing order of the engine (e.g., the cylinder number order inwhich fuel is injected into each cylinder and then combusted). Asdescribed further below with reference to FIGS. 3-4, the controller mayadjust fueling to the engine cylinders and/or diagnose a condition ofthe fuel injectors based on the received data from the torque outputsensor.

Since the engine includes one knock sensor for each cylinder, eachindividual cylinder knock sensor may measure data associated with thecylinder it is coupled to. In one example, the knock sensor may be astrain gauge based or accelerometer based knock sensor. The knock sensormay output a voltage which is then received as a voltage signal at thecontroller. In one embodiment, the controller processes the voltagesignal from the knock sensor to determine a corresponding indicated meaneffective pressure (IMEP) value and/or peak cylinder pressure (PCP)value (or a maximum acceleration value associated with the PCP) for theindividual cylinder which the knock sensor is coupled to. Thus, thecontroller receives data from each knock sensor of each engine cylinderof the engine and processes the received data to indicate enginecylinder knock, determine the indicated IMEP and/or PCP, andsubsequently adjust engine operation based on the received data. Inanother example, the controller may determine cylinder misfire based onthe output of the knock sensors, a crankshaft position output (e.g., viaa crankshaft position or speed sensor, as shown in FIG. 2 and describedfurther below), and a known cylinder firing order of the engine (e.g.,the cylinder number order in which fuel is injected into each cylinderand then combusted). As described further below with reference to FIGS.3-4, the controller may adjust fueling to the engine cylinders and/ordiagnose a condition of the fuel injectors based on the received datafrom the knock sensors.

FIG. 2 depicts an embodiment of a combustion chamber, or cylinder 200,of a multi-cylinder internal combustion engine, such as the engine 104described above with reference to FIG. 1. Cylinder 200 may be arepresentative cylinder for cylinders 108 in FIG. 1. Additionally, thecylinder shown in FIG. 2 may be defined by a cylinder head 201, housingthe intake and exhaust valves and fuel injector, described below, and acylinder block 203. In some examples, each cylinder of themulti-cylinder engine may include a separate cylinder head coupled to acommon cylinder block.

The engine may be controlled at least partially by a control systemincluding controller 148 which may be in further communication with avehicle system, such as the vehicle system 100 described above withreference to FIG. 1. As described above, the controller may furtherreceive signals from various engine sensors including, but not limitedto, engine speed from a crankshaft speed sensor 209, engine load, boostpressure, exhaust pressure, ambient pressure, CO₂ levels, exhausttemperature, NO_(x) emission, engine coolant temperature (ECT) fromtemperature sensor 230 coupled to cooling sleeve 228, etc. In oneexample, the crankshaft speed sensor may be a Hall effect sensor,variable reluctance sensor, linear variable differential transducer, anoptical sensor, or other types/forms of speed sensors, configured todetermine crankshaft speed (e.g., RPM) based on the speed of one or moreteeth on a wheel of the crankshaft. In another example, the crankshaftspeed sensor may also determine a position of the crankshaft.Correspondingly, the controller may control the vehicle system bysending commands to various components such as alternator/generator,cylinder valves, air and/or fuel throttle, fuel injectors, etc.

As shown in FIG. 2, the controller receives a signal (e.g., output) fromthe crankshaft speed sensor. In one example, this signal (which may bean analog output that includes a pulse each time a tooth of the wheel ofthe crankshaft passes the crankshaft speed sensor) may be converted by aprocessor of the controller into an engine speed (e.g., RPM) signal. Thecontroller may then use the engine speed signal to adjust engineoperation (e.g., adjust primary fueling to the cylinder).

The cylinder (i.e., combustion chamber) 200 may include combustionchamber walls 204 with a piston 206 positioned therein. The piston mayinclude a piston ring and/or liner disposed between an outer wall of thepiston and the inner wall of the cylinder. The piston 206 may be coupledto a crankshaft 208 so that reciprocating motion of the piston istranslated into rotational motion of the crankshaft. In someembodiments, the engine may be a four-stroke engine in which each of thecylinders fires (e.g., fuel is injected into each cylinder) inaccordance with a firing order during two revolutions of the crankshaft.In other embodiments, the engine may be a two-stroke engine in whicheach of the cylinders fires in a firing order during one revolution ofthe crankshaft.

The cylinder 200 receives intake air for combustion from an intakeincluding an intake runner (or manifold) 210. The intake runner 210receives intake air via an intake manifold. The intake runner 210 may beconfigured such that there is one runner per cylinder or such that asingle intake runner communicates with multiple cylinders (e.g. onerunner per bank of a V-engine which communicates with all cylinders on abank, wherein the V-engine consists of two runners) of the engine inaddition to the cylinder, for example, or the intake runner 210 maycommunicate exclusively with that one cylinder.

Exhaust gas resulting from combustion in the engine is supplied to anexhaust including an exhaust runner 212. Exhaust gas flows through theexhaust runner 212, to a turbocharger in some embodiments (turbochargernot shown in FIG. 2) and to atmosphere, via an exhaust manifold. Theexhaust runner 212 may further receive exhaust gases from othercylinders of the engine in addition to the single cylinder (as shown),for example.

Each cylinder of the engine may include one or more intake valves andone or more exhaust valves. For example, the cylinder in FIG. 2 is shownincluding at least one intake poppet valve 214 and at least one exhaustpoppet valve 216 located in an upper region of cylinder. In someembodiments, each cylinder of the engine may include at least two intakepoppet valves and at least two exhaust poppet valves located at thecylinder head.

The intake valve 214 may be controlled by the controller via an actuator218. Similarly, the exhaust valve 216 may be controlled by thecontroller via an actuator 220. During some conditions, the controllermay vary the signals provided to the actuators 218 and 220 to controlthe opening and closing of the respective intake and exhaust valves. Theposition of the intake valve 214 and the exhaust valve 216 may bedetermined by respective valve position sensors 222 and 224,respectively. The valve actuators may be of the electric valve actuationtype or cam actuation type, or a combination thereof, for example.

The intake and exhaust valve timing may be controlled concurrently orany of a possibility of variable intake cam timing, variable exhaust camtiming, dual independent variable cam timing or fixed cam timing may beused. In other embodiments, the intake and exhaust valves may becontrolled by a common valve actuator or actuation system, or a variablevalve timing actuator or actuation system. Further, the intake andexhaust valves may by controlled to have variable lift by the controllerbased on operating conditions.

In some embodiments, each cylinder of the engine may be configured withone or more fuel injectors for providing fuel thereto (as shown in FIG.1). As a non-limiting example, FIG. 2 shows the cylinder including afuel injector 226. The fuel injector 226 is shown coupled directly tothe cylinder for injecting fuel directly therein. In this manner, fuelinjector 226 provides what is known as direct injection of a fuel intothe cylinder. The fuel may be delivered to the fuel injector 226 from ahigh-pressure fuel system including a fuel tank 232, fuel pumps, and afuel rail (not shown). In one example, the fuel is diesel fuel that iscombusted in the engine through compression ignition. In othernon-limiting embodiments, the fuel may be gasoline, kerosene, jet fuel,heavy hydrocarbon oils derived from petroleum crudes, heavynon-petroleum hydrocarbon oils, heavy biodiesel, or other petroleumdistillates of similar density through compression ignition (and/orspark ignition). In other embodiments, the fuel may be a combination oftwo or more of these different types of fuel. In yet other embodiments,ignition of the fuel-air mixture is achieved through the use of laser orplasma ignitors. Further, each cylinder of the engine may be configuredto receive gaseous fuel (e.g., natural gas) alternative to or inaddition to diesel fuel. The gaseous fuel may be provided to thecylinder via the intake manifold, as explained below, or other suitabledelivery mechanism or mechanisms such as multi-port injection of gaseousfuel very close to the intake valve(s) of each cylinder or directinjection of gaseous fuel in to the engine cylinder.

Turning to FIG. 3, a method 300 for adjusting fuel injection of one ormore fuel injectors of an engine based on a response in an engineoperating parameter following a fuel injector injection event is shown.As explained above, at least one fuel injector may be coupled to eachcylinder (such as fuel injectors 111 shown in FIG. 1 and/or fuelinjector 226 shown in FIG. 2). Further, each fuel injector of eachcylinder may fire (e.g., inject fuel) at a different time in a singleengine cycle according to a cylinder firing order of the engine (e.g.,cylinder 1, cylinder 2, cylinder 3 . . . ). Accordingly, after eachinjection of fuel into a cylinder, an engine operating parameter maychange in response to the injection. This change in engine operatingparameter may be used to determine a change in performance of one ormore of the fuel injectors from what is expected. Instructions forcarrying out method 300 and the rest of the methods included herein maybe executed by a controller (such as controller 148 shown in FIGS. 1-2)based on instructions stored in the memory of the controller and inconjunction with signals received from sensors of the engine system,such as the sensors described above with reference to FIGS. 1-2 (e.g.,knock sensors 110 and crankshaft speed sensor 209). The controller mayemploy engine actuators of the engine system (such as actuators of fuelinjectors) to adjust engine operation, according to the methodsdescribed below.

At 302, the method includes estimating and/or measuring engine operatingconditions. Engine operating conditions may include one or more ofengine speed, engine torque output, a knock level, misfire indication,engine load, mass air flow, engine temperature, ambient pressure,ambient temperature, peak cylinder pressure (PCP), indicated meaneffective pressure (IMEP), or the like. At 304, the method includesdetermining whether it is time for a fuel injector diagnostic. In oneexample, a fuel injector diagnostic may be requested or performedautomatically after a duration of engine operation, a number of enginecycles, a number of fuel injection events for each fuel injector, and/ora distance of vehicle travel. In another embodiment, a fuel injectordiagnostic may be performed during each engine cycle. In yet anotherembodiment, a fuel injector(s) diagnostic may be performed either justafter engine start-up, or just before engine shut-down, or both start-upand shut-down. If it is not time to perform the fuel injectordiagnostic, the method continues to 306. At 306, the method includesinjecting fuel via one or more fuel injectors into each cylinder basedon a previous fuel injector diagnostic and current engine operatingconditions. As explained further below, during a fuel injectordiagnostic, the performance of the fuel injectors may be determined andcompared to expected values. If the fuel injector performance of one ormore fuel injectors is different than expected (but still within theconfines of pre-defined lower limit and upper limit of performance), thecontroller may adjust fuel injection (e.g., via adjusting a pulse widthof fuel injected by the fuel injector) to deliver a desired amount offuel and account for the change in performance.

Alternatively, at 304, if it is time for a fuel injector diagnostic, themethod continues to 308 to determine whether to use a pilot injectionfor the diagnostic. In one example, as explained further below, a pilotinjection may be performed via a fuel injector, in addition to andbefore the primary fuel injection (e.g., main injection). For example,the primary fuel injection may inject a larger pulse of fuel during acompression stroke of the cylinder (e.g., in a four-stroke cycle whichincludes intake, compression, combustion, and exhaust strokes) and thepilot injection may inject a smaller pulse of fuel separate from andprior to the primary fuel injection during the same cycle of the samecylinder. In one example, the pilot injection method for diagnosing fuelinjector performance may be used when set operating conditions forperforming the diagnostic are met. In one example, the set operatingconditions may include a selected notch level or range of notch levels(e.g., notch eight), engine speed within a threshold range (e.g.,between a lower threshold engine speed and an upper threshold enginespeed), and/or an engine power level within a threshold range (e.g.,between a lower threshold power level and an upper threshold powerlevel).

If the conditions for diagnosing the fuel injectors via pilot injectionat 308 are not met, the method continues to 320. At 320, the methodincludes injecting fuel into each cylinder of the engine and diagnosingthe fuel injectors based on a variation in engine speed accelerationbetween the engine cylinders. The method at 320 is expanded upon inmethod 500 of FIG. 5, as described further below. Alternatively, at 308,if the conditions for diagnosing the fuel injectors via pilot injectionare met, the method continues to 310 to select an individual cylinder orgroup of cylinders for pilot injection. In one embodiment, only onecylinder may receive a pilot injection via its fuel injector during asingle engine cycle. For example, during a single engine cycle includingperforming a primary injection at each cylinder, according to thecylinder firing order, only one fuel injector of one cylinder mayadditionally perform the pilot injection. In this way, an engineoperating parameter response due to the pilot injection may beregistered and correlated to the one fuel injector that performed thepilot injection. As such, only one fuel injector of one cylinder may bediagnosed at a time (e.g., during a single engine cycle). The method at310, 312, and 314 may then be repeated for each fuel injector of eachcylinder during different engine cycles, as explained further below. Inanother embodiment, more than one cylinder may receive the pilotinjection during a single engine cycle. However, these cylinders may beadequately and/or significantly separated from one another in thecylinder firing order (e.g., they may not be fired sequentially, oneafter the other) so that the engine operating parameter response due toeach pilot injection may be correlated to the correct fuel injector orfuel injectors. In this way, a subset (single or group) of the enginecylinders may receive the pilot injection during the same engine cyclebut at different times during that engine cycle.

After selecting the cylinder(s) and corresponding fuel injector(s) forthe pilot injection, the method continues to 312 to perform the pilotinjection at the selected cylinder (or cylinders) and diagnose the fuelinjector(s) according to the method 400 presented at FIG. 4 (asdescribed further below). As explained further below, in one example,diagnosing the fuel injector may include determining an effective pulsewidth of the pilot injection for achieving a pre-defined engineparameter (such as engine speed), comparing it to an expected pulsewidth, and determining degradation or a change in performance of thefuel injector based on how the effective pulse width changes over time.Following performing the pilot injection, the method continues to 314 toperform the primary fuel injection at the selected cylinder and allother cylinders of the engine (unless one or more cylinders are beingskip fired). After all firing cylinders have been fired (via primaryfuel injection) during the engine cycle, the method continues to 316 todetermine whether the fuel injector diagnostic should be repeated forone or more of the other cylinders (and corresponding fuel injectors).If the diagnostic should be repeated, the method circles back to 310.

However, if the diagnostic is not to be repeated for the other cylinders(e.g., if the diagnostic has already been performed for all fuelinjectors), the method continues to 318 to adjust subsequent fuelinjections (e.g., subsequent primary injections during the next orfollowing engine cycles for the diagnosed fuel injectors) based on theresults of the diagnosis. For example, the method at 318 may includeadjusting the amount of fuel or pulse width of fuel injected via theprimary injection of a diagnosed fuel injector based on a determinedengine speed, engine torque output, engine knock, or engine misfireresponse during the pilot injection (if continuing from 318) or theengine speed acceleration response during injecting fuel into eachcylinder (if continuing from 320). For example, the controller maydetermine a control signal to send to the fuel injector actuator, suchas an updated primary pulse width of the signal being determined basedon a determination of the engine operating parameter response during thediagnostic routine. The controller may determine the pulse width througha determination that directly takes into account a determined effectivepulse width (as described further below with regard to method 400) or adetermined engine speed acceleration (as described further below withregard to method 500), such as decreasing the primary effective pulsewidth or decreasing engine speed acceleration. The controller mayalternatively determine the pulse width based on a calculation using alook-up table with the input being the effective pulse width, engineoperating parameter response to the pilot injection, and/or the enginespeed acceleration, and the output being the new or updated or commandedpulse-width.

In one embodiment of method 300, each of the methods at 312 and 320 mayadditionally include controlling a turbocharger (such as turbocharger120 shown in FIG. 1) and/or an amount of intake air entering the enginecylinders to a steady-state level. For example, this may includeoperating the turbocharger at a steady (and not changing) boost level.In another example, this may include maintaining a position of an airthrottle in the intake passage at a set position. As a result, theair-fuel ratio entering the engine cylinders may not change during thetesting (e.g., diagnosing) period due to the airflow.

FIG. 4 shows a method 400 for diagnosing a condition of a fuel injectorbased on a response in an engine operating parameter followingperforming a pilot injection with the fuel injector. Method 400 maycontinue from the method at 312 in FIG. 3. As such, method 400 begins at402 by injecting a first pulse of fuel as a pilot injection into theselected cylinder(s). For example, the method at 402 may includeinjecting the first pulse of fuel via a first fuel injector coupled tothe selected cylinder. In one example, the method at 402 may alsoinclude determining an amount or pulse width of the first pulse. Theamount or pulse width of the first pulse of fuel may be smaller than asecond pulse of fuel injected during the primary injection event of thefirst fuel injector (e.g., the primary injection being a main injectionoccurring separate from and after the pilot injection, as explainedabove). In another example, the amount or pulse width of the first pulseof fuel may be selected based on an amount of fuel that will cause adetectable change in an engine operating parameter (for diagnosing thefuel injector). For example, the first pulse of fuel must be largeenough so that an engine speed sensor may detect a change in enginespeed from a baseline engine speed after performing the pilot injection.After performing the pilot injection at 402, the method continues to404.

At 404, the method includes correlating a response in an engineoperating parameter to the pilot injection. As explained above, afterinjecting the first pulse of fuel as the pilot injection via the firstfuel injector, an engine operating parameter may change due to (e.g., inresponse to) the pilot injection. This change from baseline of theengine operating parameter may then be correlated with the pilotinjection. As one example, the engine operating parameter may be enginespeed and the response in the engine operating parameter may be anincrease (e.g., spike) in engine speed from a baseline engine speed(prior to the pilot injection) to engine speed after the pilotinjection. As another example, the engine operating parameter may be theengine torque output measured via a torque sensor coupled to the enginecrankshaft. The measured torque level may register the actual combustionnoise due to the pilot injection. As one example, the response in theengine operating parameter may be the change in the torque leveldetermined from the torque sensor output. In yet another example, theengine operating parameter may be a misfire level or indicationdetermined from an output of the torque sensor. As another example, theengine operating parameter may be a knock level output via a knocksensor coupled to the cylinder that the first fuel injector is coupledto. The knock level may register the actual combustion noise due to thepilot injection. As one example, the response in the engine operatingparameter may be the change in the IMEP or PCP determined from the knocksensor output. In yet another example, the engine operating parametermay be a misfire level or indication determined from an output of theknock sensor.

At 406, the method includes determining the effective pulse width of thepilot injection of the fuel injector of the selected cylinder(s) basedon the response in the engine operating parameter determined at 404. Inone example, determining the effective pulse width may include thecontroller making a logical determination of the effective pulse widthof the pilot injection based on logic rules that are a function of theengine operating parameter (e.g., engine speed, engine torque output,engine knock, IMEP, PCP, and/or engine misfire). As one example, thecontroller may receive the engine speed signal from the engine speedsensor before, during, and after the pilot injection, determine thechange in the engine speed signal from the baseline engine speed due tothe pilot injection, and determine (e.g., calculate as a function of thechange in engine speed or use a look-up table with the input being thechange in engine speed due to the pilot injection) the effective pulsewidth of the pilot injection. In another example, the controller maycompare the knock signature received from the knock sensor following thepilot injection to a reference knock sensor signature and then determinethe effective pulse width. For example, the controller may determine theeffective pulse width as a function of the measured knock signaturefollowing the pilot injection and the reference knock signature.

At 408, the method includes injecting a second pulse of fuel as aprimary injection into the selected cylinder(s) and adjusting theprimary injection based on the determined effective “primary” pulsewidth. For example, the controller may compare the determined effectivepulse width to the commanded pulse width for the first amount of fuel ofthe pilot injection. If the effective pulse width was larger thancommanded, then too much fuel may have been injected via the firstinjector. Alternatively, if the effective pulse width was smaller thancommanded, then too little fuel may have been injected via the firstinjector. As a result, the controller may compensate for this differenceby adjusting the primary injection amount (e.g., increase if theeffective pilot pulse width was too small and decrease if the effectivepilot pulse width was too large). Specifically, the controller may makea logical determination of the pulse width of the second pulse of fuelfor the primary injection of the selected cylinder based on logic rulesthat are a function of the determined effective pilot pulse width. Inthis way, the controller may correct/adjust subsequent fuel injectionswith the injector of the selected cylinder to account for degradation,aging, or faults of the fuel injector or fuel injector components (e.g.,nozzle fuel spray holes, solenoids, or the like).

At 410, the method includes monitoring (e.g., tracking) the effectivepulse width of the fuel injector over time. For example, for each pilotinjection event (during the injector diagnostic) of a single fuelinjector, the controller may determine the effective pulse width andtrack changes to the effective pilot pulse width over time and over anumber of pilot injections. For example, FIG. 6 shows a graph 600 ofexample changes to an effective pulse width of a fuel injector over timeand a number of pilot injection events. Specifically, graph 600 shows afirst plot 602 of a baseline effective pulse width that does not changesignificantly (e.g., greater than a threshold amount of change) overtime. Graph 600 also shows a second plot 604 where the effective pulsewidth increases over time and a third plot 606 where the effective pulsewidth decreases over time. At time t1, the effective pulse width of thesecond plot 604 and the third plot 606 begin changing and at time t2 theeffective pulse widths of these two plots may change by an amount thatexceeds the threshold amount of change. As a result, the controller mayindicate degradation or a change in performance of the fuel injector, asexplained further below.

Returning to FIG. 4, at 412 the method includes determining if theeffective pulse width is increasing (e.g., as shown at plot 604 in FIG.6). In one example, the controller may determine the effective pulsewidth is increasing if a rate of change of the effective pulse width isgreater than a threshold rate of change. In another example, thecontroller may determine the effective pulse width is increasing if themost recent effective pulse width value is a threshold amount differentthan a previous effective pulse width value or an original effectivepulse width value (e.g., the effective pulse width when the injector wasnew or used for the very first time for a pilot injection). If theeffective pulse width is increasing, the method continues to 414 toindicate a change in performance of the fuel injector. As one example,the method at 414 may include indicating one or more of a decrease inresponse time of a solenoid of the fuel injector and/or a clogged ordegraded fuel injector. In one example, the controller may send anotification (e.g., audible or visual) to a vehicle operator that thefuel injector needs to be serviced or replaced. Alternatively, at 412,if the effective pilot pulse width is not increasing, the methodcontinues to 416 to determine if the effective pilot pulse width isdecreasing (similar to as explained above for 412). If the effectivepulse width is decreasing, the method continues to 418 to indicate oneor more of an increase in a size of one or more nozzle fuel spray holesof the fuel injector and/or a faulty injector/injection. The controllermay then send an indication to the vehicle operator, as described above.If the effective pilot pulse width is not increasing and/or notdecreasing, the method instead continues to 420 to not indicatedegradation of the fuel injector and to continue (normally) injectingfuel with the fuel injector.

Method 400 may be repeated for each cylinder (and fuel injector coupledto each cylinder) during different engine cycles. An example ofperforming pilot injections via two fuel injectors of two differentcylinders during different engine cycles is shown in FIG. 7.Specifically, FIG. 7 shows a graph 700 showing fuel injection events ata first cylinder at plot 702, fuel injection events at a second cylinderat plot 704, fuel injection events at a third cylinder at plot 706, andchanges in engine speed at plot 708. In the example shown in FIG. 4, thecylinder firing order may be cylinder 1-cylinder 2-cylinder 3. Prior totime t1, the controller may determine that it is time to perform adiagnostic of a first fuel injector coupled to the first cylinder. Assuch, at time t1, the first fuel injector injects a first pulse of fuelas a pilot injection into the first cylinder (plot 702). In response toinjecting the first pulse of fuel, engine speed increases from thebaseline value prior to the pilot injection (plot 708). During the pilotinjection, no other cylinders are receiving fuel injections (e.g., noother fuel injectors are firing). At time t2, a duration after time t1,the controller actuates the first fuel injector to inject a second pulseof fuel as the primary injection into the first cylinder (plot 702).Since the engine speed response following the pilot injection may besmaller than expected for the commanded first pulse of fuel, thecontroller may increase the second pulse of fuel above a previouslycommanded amount (e.g., the amount of fuel injection for the primaryinjection at the first cylinder is larger than for the other cylindersin the firing order). In response to the injecting of the second“primary” pulse of fuel, engine speed increases. The increase in enginespeed due to the primary injection is larger than the increase in enginespeed due to the pilot injection since the second pulse of fuel isgreater than the first pulse of fuel (as denoted by the height of thearrows in plot 702). The next cylinder in the firing order, cylinder 2,receives its primary injection of fuel via a second fuel injector attime t3 and then cylinder 3 receives its primary injection of fuel via athird fuel injector at time t4.

After time t4, the controller may determine that it is time to perform adiagnostic of the second fuel injector coupled to the second cylinder.As shown at time t5, the first fuel injector again injects fuel, butonly as a primary injection, into the first cylinder. Additionally, theamount of fuel injected during the primary injection at time t5 isgreater than the amount of fuel injected during the primary injectionsat the other cylinders. The second injector then injects a smaller,first pulse of fuel (at time t6) as the pilot injection into the secondcylinder and then, at time t7, a larger, second pulse of fuel as theprimary injection into the second cylinder. During the pilot injectioninto the second cylinder, no other fuel injectors of the other cylindersare injecting fuel. Finally, the third cylinder receives the primaryinjection of fuel from the third fuel injector at time t8. In this way,a pilot injection of fuel may be used to diagnose fuel injectors ofdifferent engine cylinders during different engine cycles. As a result,engine speed responses may be correlated to the pilot injection for thesingle cylinder receiving the pilot injection and then used to diagnosethe performance of the fuel injector.

Turning to FIG. 5, a method 500 for diagnosing a condition of one ormore fuel injectors based on a variation in engine speed accelerationsafter injecting fuel into each cylinder is shown. Method 500 maycontinue from the method at 320 in FIG. 3. As such, method 500 begins at502 by injecting fuel into each cylinder over a single engine cycle. Forexample, every cylinder may receive a primary injection of fuel, at itstime in the firing order, via the fuel injector coupled thereto. As aresult, every fuel injector may fire once in the single engine cycle. At504, the method includes determining individual engine speedaccelerations resulting from the injection of fuel into each cylinder.For example, as shown in FIG. 7, every time fuel is injected into acylinder, engine speed may increase (and accordingly the acceleration ofthe engine speed increases proportional to injected fuel quantity). Thecontroller may receive the engine speed signal from an engine speedsensor during all the injection events and then correlate each enginespeed acceleration (e.g., each peak in engine speed) to each fuelinjector/cylinder based on the known firing order of the cylinders. As aresult, the controller may make a logical determination of theindividual engine speed accelerations for each fuel injector/cylinderbased on logic rules that are a function of the received (e.g.,measured) engine speed signal and the known firing order.

At 506, the method includes comparing the individual engine speedacceleration values for each fuel injector/cylinder and determining thevariation in engine speed accelerations between the cylinders. In oneexample, a same amount of fuel may be injected into each cylinder viaeach corresponding fuel injector at 502. In another example, differentamounts of fuel may be injected into each cylinder (e.g., due tovariations in aging/deterioration/degradation of performance orcharacteristics of the fuel injectors). However, in both examples,approximately the same engine speed acceleration response may beexpected due to fuel injection at each cylinder. In one example,determining the variation in the engine speed accelerations between thecylinders may include the controller calculating a standard deviationbetween the determined individual engine speed accelerationscorresponding to each cylinder (e.g., each fuel injection event at eachcylinder). At 508, the method includes determining whether the variationdetermined at 506 is greater than a threshold level. In one example, thethreshold level may be a level that indicates a change in performance ordegradation of one or more of the fuel injectors relative to theremaining fuel injectors. In one example, the allowable variation infueling quantity (injection event-to-injection event orinjector-to-injector) is within +1-1.5% of nominal quantity when theinjector is new. In this example, the allowable variation on thresholdprior to condemning an in-use injector and/or changing to a new injectoris +/−3% or higher of nominal quantity.

If the determined variation is not greater than the threshold level, themethod continues to 510 to not indicate degradation of the fuelinjectors and to instead continue injecting fuel via the fuel injectorsbased on engine operating conditions. Alternatively, at 508, if thevariation is greater than the threshold level, the method continues to512 to indicate degradation of one or more of the fuel injectors andthen identify which fuel injector (or injectors) is degraded based onthe individual engine speed acceleration and the known engine cylinderfiring order. For example, the controller may know the crankshaftposition (e.g., angle) at which each individual engine speedacceleration occurred (from an output of a crankshaft position or speedsensor). By comparing this to the known firing order and a known crankangle at which each fuel injector of each cylinder fires, the controllermay determine which individual engine speed acceleration belongs towhich specific cylinder (and the corresponding fuel injector). Thecontroller may then determine which engine speed acceleration deviatedfrom the other engine speed accelerations (or an average value of all ofthe engine speed accelerations) and then indicate degradation of thecorresponding fuel injector (e.g., the fuel injector that injected fuelwhich corresponds to engine speed acceleration that varied the greatestamount or a threshold amount from the average).

At 514, the method includes determining if the identified engine speedacceleration resulting from injection via the indicated fuel injector isgreater than an expected engine speed acceleration. In one example, theexpected engine speed acceleration may be an average engine speedacceleration of all the engine cylinders. In another example, theexpected engine speed acceleration may be determined from a look-uptable with the commanded fuel injection amount (or pulse width) as theinput and the expected engine speed acceleration as the output. If theengine speed acceleration of the indicated fuel injector is greater thanthe expected engine speed acceleration, the method continues to 516 toindicate injection error and/or an increase in a size of one or morenozzle holes of the injector (e.g., since this may mean too much fuelwas injected via the identified fuel injector). In one example, theindication/action at 516 may include the controller sending an audibleor visual indication to the vehicle operator that the fuel injectorneeds to be serviced or replaced. Alternatively, at 514, if the enginespeed acceleration of the indicated fuel injector is not greater than(e.g., is less than) the expected engine speed acceleration, the methodcontinues to 518 to indicate one or more of a clogged fuel injector,mechanical degradation of the fuel injector, and/or degradation of asolenoid of the fuel injector.

In this way, the technical effect of diagnosing a condition orindicating degradation of one or more fuel injectors of the engine isidentifying a degraded or malfunctioning injector before more seriousdegradation of the engine or ceasing of functioning of the injectoroccurs. Further, by identifying which injector is experiencing a changein performance (as determined by correlating a change in response in anengine operating parameter following a pilot injection into one enginecylinder or a comparison of primary injections of fuel into all enginecylinders), the controller may take corrective action to compensate forthe change in performance. For example, the controller may adjust fuelinjection to account for a changing effective pulse width of one or moreof the injectors. By identifying which injector is degraded, only thedegraded injector may be serviced or replaced (and not every single fuelinjector). This may reduce repair and/or replacement costs. Further, iffuel injectors continue to be functional past their specified lifetime,they may continue to be used, rather than automatically replaced at apre-defined usage period (such as A months or B mega-watt hours),thereby saving additional part costs.

As one embodiment, a method for an engine comprises injecting a firstpulse of fuel as a first pilot injection into a first subset ofcylinders of a plurality of engine cylinders, where the first pilotinjection precedes a primary injection of fuel into the first subset ofcylinders by a duration; correlating a first response in an engineoperating parameter to the first pilot injection; and adjusting theprimary injection of fuel into the first subset of cylinders based onthe first response. In one example, the first subset of cylindersincludes a single cylinder, injecting the first pulse of fuel includesinjecting the first pulse of fuel as the first pilot injection into onlythe single cylinder via a first fuel injector, and the method furthercomprises diagnosing a condition of the first fuel injector based on achange in the first response over a number of first pilot injections.The method may further comprise estimating an effective pulse width ofthe first fuel injector based on the first response for the number offirst pilot injections and diagnosing the condition of the first fuelinjector based on a change in the estimated effective pulse width overthe number of first pilot injections. In one example, diagnosing thecondition of the first fuel injector includes indicating an increase ina size of one or more nozzle fuel spray holes of the first fuel injectorin response to the estimated effective pilot pulse width decreasing overthe number of first pilot injections. In another example, diagnosing thecondition of the first fuel injector includes indicating one or more ofa decrease in response time of a solenoid of the first fuel injector ormechanical degradation of the first fuel injector in response to theestimated effective pulse width increasing over the number of firstpilot injections. For example, the adjustment/correction may include theeffective pilot pulse width being increased over the number of firstpilot injections. Alternately, the response may include an increase inthe rise-rate of the pilot pulse. In one example, the method may furthercomprise, at a different time during engine operation than injecting thefirst pulse of fuel, injecting a second pulse of fuel as a second pilotinjection into a second subset of cylinders of the plurality of enginecylinders via one or more fuel injectors, where the second pilotinjection precedes a primary injection of fuel into the second subset ofcylinders by a pre-defined duration. The method may further comprisecorrelating a second response in the engine operating parameter to thesecond pilot injection, adjusting the primary injection of fuel into thesecond subset of cylinders based on the second response, and diagnosingthe one or more fuel injectors based on a change in the second responseover a number of second pilot injections. Further, in one example, thefirst pilot injection and the second pilot injection occur duringdifferent engine cycles where a primary injection of fuel is injectedinto each cylinder of the plurality of engine cylinders. In anotherexample, the engine operating parameter is one of a knock level outputby a knock sensor coupled to the first subset of cylinders, an enginespeed output by an engine speed sensor coupled to a crankshaft of theengine, or an engine torque output measured by an engine torque sensorcoupled to the crankshaft of the engine. The method may further comprisedelivering the first pilot injection and the primary injection of fuelinto the first subset of cylinders via one or more fuel injectors andadjusting the primary injection of fuel into the first subset ofcylinders based on the first response may include determining aneffective pulse width of the first pilot pulse of fuel based on thefirst response and adjusting a pulse width of the primary injection offuel delivered by the one or more fuel injectors based on the determinedeffective pulse width. The method may further comprise injecting asecond pulse of fuel as the primary injection of fuel into the firstsubset of cylinders, where the first pulse of fuel is smaller than thesecond pulse of fuel and where the first pulse of fuel and the secondpulse of fuel are separated from one another by a pre-set spacing intime or crank angle. In another example, the method may further compriseinjecting the first pulse of fuel as the first pilot injection into thefirst subset of cylinders in response to the engine operating at aselected notch level and at an engine speed within a threshold enginespeed range. In still another example, injecting the first pulse of fuelas the first pilot injection occurs during a first engine cycle where aprimary injection of fuel is injected into each cylinder of theplurality of engine cylinders and the first pilot injection of the firstpulse of fuel is only injected into the first subset of cylinders, themethod may further comprise, during a different, second engine cycle,not injecting the first pulse of fuel as the first pilot injection intothe first subset of cylinders and injecting a second pulse of fuel asthe primary injection into the first subset of cylinders, and whereduring the second engine cycle, the second pulse of fuel is larger thanduring the first engine cycle. In one example, the second pulse of fuelis larger than during the first engine cycle because 100% of the energyto power the engine and maintain engine speed and engine torque, isachieved via this single pulse versus a combination of the first pilotfuel pulse and the second primary fuel pulse.

As another embodiment, a method for an engine comprises injecting fuelinto each cylinder of a plurality of cylinders of the engine over asingle engine cycle via a plurality of fuel injectors, where each fuelinjector of the plurality of fuel injectors is coupled to a differentcylinder of the plurality of cylinders; determining individual enginespeed accelerations resulting from the injection of fuel into eachcylinder; and indicating degradation of one or more of the plurality offuel injectors in response to a variation in the determined individualengine speed accelerations being greater than a threshold accelerationlevel. In one example, the method may further comprise indicating whichfuel injector of the plurality of fuel injectors is degraded based onthe individual engine speed accelerations and a known engine cylinderfiring order of the engine. In another example, indicating degradationincludes: indicating an increase in a size of one or more nozzle fuelspray holes of the indicated fuel injector in response to the individualengine speed acceleration resulting from the injection of fuel via theindicated fuel injector being greater than an expected engine speedacceleration for a non-degraded fuel injector; and indicating one ormore of a decrease in response time of a solenoid of the indicated fuelinjector or mechanical degradation of the indicated fuel injector inresponse to the individual engine speed acceleration resulting from theinjection of fuel via the indicated fuel injector being less than theexpected engine speed acceleration.

As yet another embodiment, a system for an engine comprises a pluralityof engine cylinders including at least a first cylinder and a secondcylinder; a first fuel injector coupled to the first cylinder; a secondfuel injector coupled to the second cylinder; and a controller withcomputer readable instructions for: during a first engine cycle,injecting a primary pulse of fuel into the first cylinder via the firstfuel injector and the second cylinder via the second fuel injector andinjecting a pilot pulse of fuel, before the primary pulse, into only thefirst cylinder via the first fuel injector; correlating a first responsein an engine operating parameter to injection of the pilot pulse of fuelinto the first cylinder; and during a second engine cycle, following thefirst engine cycle, adjusting the primary pulse of fuel into the firstcylinder based on the first response to the pilot pulse of fuel. In oneexample, the computer readable instructions further include instructionsfor: during a third engine cycle, injecting the primary pulse of fuelinto the first cylinder via the first fuel injector and the secondcylinder via the second fuel injector and injecting the pilot pulse offuel, before the primary pulse, into only the second cylinder via thesecond fuel injector; correlating a second response in the engineoperating parameter to injection of the pilot pulse of fuel; and duringa fourth engine cycle, following the third engine cycle, adjusting theprimary pulse of fuel into the second cylinder based on the secondresponse to the pilot pulse of fuel. In another example, the system mayfurther comprise a real-time engine torque output sensor coupled to acrankshaft of the engine, where the engine operating parameter is atorque signal output by the torque output sensor, and where the computerreadable instructions further include instructions for diagnosing acondition of the first injector in response to a change in the torqueoutput over a number of engine cycles when the pilot pulse of fuel isinjected into the first cylinder via the first fuel injector. In yetanother example, the system may further comprise a knock sensor coupledto the first cylinder, where the engine operating parameter is a knocksignal output by the knock sensor, and where the computer readableinstructions further include instructions for diagnosing a condition ofthe first injector in response to a change in the knock signal over anumber of engine cycles when the pilot pulse of fuel is injected intothe first cylinder via the first fuel injector.

As used herein, an element or step recited in the singular and proceededwith the word “a” or “an” should be understood as not excluding pluralof said elements or steps, unless such exclusion is explicitly stated.Furthermore, references to “one embodiment” of the invention do notexclude the existence of additional embodiments that also incorporatethe recited features. Moreover, unless explicitly stated to thecontrary, embodiments “comprising,” “including,” or “having” an elementor a plurality of elements having a particular property may includeadditional such elements not having that property. The terms “including”and “in which” are used as the plain-language equivalents of therespective terms “comprising” and “wherein.” Moreover, the terms“first,” “second,” and “third,” etc. are used merely as labels, and arenot intended to impose numerical requirements or a particular positionalorder on their objects.

The control methods and routines disclosed herein may be stored asexecutable instructions in non-transitory memory and may be carried outby the control system including the controller in combination with thevarious sensors, actuators, and other engine hardware. The specificroutines described herein may represent one or more of any number ofprocessing strategies such as event-driven, interrupt-driven,multi-tasking, multi-threading, and the like. As such, various actions,operations, and/or functions illustrated may be performed in thesequence illustrated, in parallel, or in some cases omitted. Likewise,the order of processing is not necessarily required to achieve thefeatures and advantages of the example embodiments described herein, butis provided for ease of illustration and description. One or more of theillustrated actions, operations and/or functions may be repeatedlyperformed depending on the particular strategy being used. Further, thedescribed actions, operations and/or functions may graphically representcode to be programmed into non-transitory memory of the computerreadable storage medium in the engine control system, where thedescribed actions are carried out by executing the instructions in asystem including the various engine hardware components in combinationwith the electronic controller.

This written description uses examples to disclose the invention,including the best mode, and also to enable a person of ordinary skillin the relevant art to practice the invention, including making andusing any devices or systems and performing any incorporated methods.The patentable scope of the invention is defined by the claims, and mayinclude other examples that occur to those of ordinary skill in the art.Such other examples are intended to be within the scope of the claims ifthey have structural elements that do not differ from the literallanguage of the claims, or if they include equivalent structuralelements with insubstantial differences from the literal languages ofthe claims.

1-13. (canceled)
 14. A method for an engine, comprising: injecting fuelinto each cylinder of a plurality of cylinders of the engine over asingle engine cycle via a plurality of fuel injectors, where each fuelinjector of the plurality of fuel injectors is coupled to a differentcylinder of the plurality of cylinders; determining individual enginespeed accelerations resulting from the injection of fuel into eachcylinder; and indicating degradation of one or more of the plurality offuel injectors in response to a variation in the determined individualengine speed accelerations being greater than a threshold accelerationlevel.
 15. The method of claim 14, further comprising indicating whichfuel injector of the plurality of fuel injectors is degraded based onthe individual engine speed accelerations and a known engine cylinderfiring order of the engine.
 16. The method of claim 15, whereinindicating degradation includes: indicating an increase in a size of oneor more nozzle fuel spray holes of the indicated fuel injector inresponse to the individual engine speed acceleration resulting from theinjection of fuel via the indicated fuel injector being greater than anexpected engine speed acceleration for a non-degraded fuel injector; andindicating one or more of a decrease in response time of a solenoid ofthe indicated fuel injector or mechanical degradation of the indicatedfuel injector in response to the individual engine speed accelerationresulting from the injection of fuel via the indicated fuel injectorbeing less than the expected engine speed acceleration.
 17. A system foran engine, comprising: a plurality of engine cylinders including atleast a first cylinder and a second cylinder; a first fuel injectorcoupled to the first cylinder; a second fuel injector coupled to thesecond cylinder; and a controller operatively coupled to the first andsecond fuel injectors and configured to: during a first engine cycle,control injection of a primary pulse of fuel into the first cylinder viathe first fuel injector and the second cylinder via the second fuelinjector and injection of a pilot pulse of fuel, before the primarypulse, into only the first cylinder via the first fuel injector;correlate a first response in an engine operating parameter to injectionof the pilot pulse of fuel into the first cylinder; and during a secondengine cycle, following the first engine cycle, adjust the primary pulseof fuel into the first cylinder based on the first response to the pilotpulse of fuel.
 18. The system of claim 17, wherein the controller isfurther configured to: during a third engine cycle, control injection ofthe primary pulse of fuel into the first cylinder via the first fuelinjector and the second cylinder via the second fuel injector andinjection of the pilot pulse of fuel, before the primary pulse, intoonly the second cylinder via the second fuel injector; correlate asecond response in the engine operating parameter to injection of thepilot pulse of fuel; and during a fourth engine cycle, following thethird engine cycle, adjust the primary pulse of fuel into the secondcylinder based on the second response to the pilot pulse of fuel. 19.The system of claim 17, further comprising a real-time engine torqueoutput sensor coupled to a crankshaft of the engine, wherein the engineoperating parameter is a torque signal output by the torque outputsensor, and wherein the controller is configured to diagnose a conditionof the first injector in response to a change in the torque output overa number of engine cycles when the pilot pulse of fuel is injected intothe first cylinder via the first fuel injector.
 20. The system of claim17, further comprising a knock sensor coupled to the first cylinder,wherein the engine operating parameter is a knock signal output by theknock sensor, and wherein the controller is configured to diagnose acondition of the first injector in response to a change in the knocksignal over a number of engine cycles when the pilot pulse of fuel isinjected into the first cylinder via the first fuel injector.
 21. Themethod of claim 14, wherein the threshold acceleration levels are basedon a commanded amount of the injection of fuel.
 22. The method of claim21, wherein the determined individual engine speed accelerations areused to determine an effective amount of fuel injected.
 23. The methodof claim 22, wherein fuel is injected into the engine via a primaryinjection and a pilot injection.
 24. The method of claim 21, wherein anamount of fuel injected is adjusted based on a difference between thedetermined individual engine speed accelerations and the thresholdacceleration level.
 25. The system of claim 17, wherein the firstresponse to the injection of the pilot pulse occurs before the primaryinjection into the first cylinder.
 26. The system of claim 17, whereinthe controller is further configured to, during a third engine cycle,control an injection of a pilot pulse of fuel of the third engine cycle,before a primary pulse of the third engine cycle, into only the firstcylinder via the first fuel injector.
 27. The system of claim 26,wherein the controller is further configured to correlate a response ofthe third engine cycle in an engine operating parameter to the injectionof the pilot pulse of the third engine cycle fuel; and determine adifference between the first response to the injection of the pilotpulse of fuel and the response of the third engine cycle.
 28. The systemof claim 27, wherein the controller is further configured to correlate aresponse of a further subsequent engine cycle in an engine operatingparameter to an injection of a pilot pulse of the further subsequentengine cycle into the first cylinder; and compare the first response tothe injection of the pilot pulse of fuel, the response of the thirdengine cycle and the further subsequent engine cycle.
 29. The system ofclaim 28, wherein the controller is further configured to adjustinjections of primary pulses into the first cylinder based on thecomparison of the first response to the injection of the pilot pulse offuel, the response of the third engine cycle and the further subsequentengine cycle.
 30. The system of claim 28, wherein the controller isfurther configured to indicate degradation when the comparisondetermines that responses to pilot injections deviate farther from athreshold with time.